The past 30 years has seen more "hot" (orange), "very hot" (red) and "extremely hot" (brown) summers, compared to a base period defined in this study from 1951 to 1980 (Source: NASA/Goddard Space Flight Center Scientific Visualization Studio)

Hotter summers have become the norm from 1980 to present compared to 1951 to 1980 (the base period)

James Hansen, study leader from NASA's Goddard Institute for Space Studies (GISS), as well as GISS researchers Makiko Sato and Reto Ruedy, have concluded that summer heat waves (mainly in the U.S. Midwest) have become the norm over the last 30 years compared to a base period 30 years before 1980 -- and it's because of global warming.

Their study works like this: the team collected mean summer temperatures from 1951 to 1980. This was considered the base period for the study. They then looked at the surface temperature data from the last 30 years (1980 until now) to determine whether extreme heat events were increasing.

From there, the team wanted to see how much heating and cooling occurred in both time periods. To do this, they used a bell curve, which is a common tool that places the middle ground at the top of the bell (for instance, if this were a grading curve, a "C" would be at the top while the next tier down on each side would be a "B" and a "D," and the bottom of the bell would be an "A" and an "F). In this case, the top of the bell would be mean temperature, the next tier down would be "cold" on one side and "hot" on the other, then "very cold" and "extremely cold" on one side moving down while "very hot" and "extremely hot" are moving down the bell on the other side.

Researchers then applied mean temperatures from 1980 until present, and found that 1980s, 1990s and 2000s fell more to the hot side than cold. The curve widened and flattened as well, which means there was a broader range of variability. This is important because Hansen once predicted that global warming's connection to extreme events would become more apparent in the decades from 1980 to present, but natural variability can play a role too and actually mask the trend. It was important to distinguish the two.

This wider curve created the new "extremely hot" category, which was barely there in the base period. However, hot has become considered normal in the last 30 years. To be more specific, 75 percent of land area on Earth had "hot" summers in the last decade alone, where only 33 percent had "hot" summers from 1951 to 1980 total.

According to the researchers, an "extremely hot" summer is considered a mean summer temperature that is experienced by less than one percent of Earth's land area during the base period. But since 2006 alone, approximately 10 percent of land area across the Northern Hemisphere had a summer like this.

"This summer, people are seeing extreme heat and agricultural impacts," said Hansen. "We're asserting that this is casually connected to global warming, and in this paper, we present the scientific evidence for that."

The study noted "extremely hot" summers in other areas besides just the U.S. Midwest, like Texas, Mexico and Oklahoma in 2011 and Eastern Europe, Western Asia and the Middle East in 2010.

This study was published in the journal Proceedings of the National Academy of Sciences.

Looks like the last of this species died in June. And even one species humans wipe out is one too many in my opinion. You can argue semantics all day long with recent numbers, and how large the extinction numbers need to be for relevance.

I think you're missing my point. One here and one there starts to add up. If you don't care, that's your right. I just don't like seeing animal or plant species disappear. And this is just how I feel about it. I have no militant stance, and am firmly in the middle about most issues.

Also, what is your opinion of global eradication of diseases? These occur (or rather, occurred) naturally and humans have seen fit to alter the natural course and remove them from the planet. Thoughts?

Listen, I am not an extremist. It sounds hypocritical but I think pathogens that harm or kill people should be controlled or eradicated if possible. Unfortunately these micro organisms are far more resilient than say, a flightless bird from New Zealand.

Looks like the last of this species died in June. And even one species humans wipe out is one too many in my opinion. You can argue semantics all day long with recent numbers, and how large the extinction numbers need to be for relevance.

So the figure you quote from Wikipedia is for a total of 12 species since 1840.

Using data from the link I included in my previous comment that looks like a bit of an under estimate, the paper I referenced gives the following:

Grand Total Extinct Mammal Species is 61 species in 500 yearsof which 58 were highly vulnerable island species (low numbers, limited habitat)

Out of a total of 4,428 known mammal species not restricted to islands (i.e. continental species) only three mammals have gone extinct in the last 500 years. These were the Bluebuck antelope, South Africa; the Algerian gazelle, Algeria; and the Omilteme cottontail rabbit, Mexico.

Grand Total Extinct Bird Species is 129 species in 500 yearsof which 123 were highly vulnerable island species (low numbers, limited habitat)

Out of a total of 8,971 known continental bird species 6 have gone extinct in 500 years.

Note that most of the extinctions above took place a long time ago, that the rate of extinctions appears to have fallen sharply in recent decades, even though the amount of specie monitoring has vastly increased.

It is worth bearing in mind that there are an estimated total of 8.7 million species on earth.

So what you have is a picture of very, very low levels of actual extinctions.

Even if the rate of extinctions were to quadruple in the next 500 years, and even if we assume that the rate of extinctions for continental species accelerates massively to match the rate of island extinctions then we get an absolutely worst case nightmare scenario of a total of 760 bird and mammal species going extinct in the next 500 years out of a total of 8.7 million species.

Frankly that doesn't seem worth worrying about. It certainly is not something that should be used as a convincing case for slowing or restricting economic development (or more accurately prolonging human poverty, suffering and premature death), nor should it be an issue which is used to whip up alarm about the impact of human activity on the environment.

The constant use of the term 'endangered species' and the banding around of wild figures for extinctions based solely on computer models and not on real world observations is a constant feature of environmentalist campaigning. It is pure propaganda and is not based on any actually observed pattern of extinction.

I honestly don't think you've bothered to read anything I wrote. I never used the words 'mass extinction', I just said man causes extinctions. That's a fact. I didn't state numbers...you did. Also, this issue is far more complex than you lead on. Just because there a a few left of a certain species does not mean everything is ok.

The only extinctions we've caused is from directly hunting a species to extinction. And guess what? Animals do this to other animals all the time thorough history.

Most of the species on your list it cannot credibly be stated that mankind has directly caused their plight. Recent DNA discoveries of some endangered species has proven a big problem is that there is not enough genetic diversity.

Also you've conveniently left out the fact that mankind has interfered with nature to preserve species that would have died out as well.

Earlier you accused me of being religious because I didn't have your point of view on this. Which is curious because you don't seem to have a very firm grasp on the evolutionary process.

I repeat the rate extinctions seems to be slowing and very, very low. Its not a big problem and there is no evidence based on real world observed data that the rate extinction is accelerating. It will be shame if some large mammals go extinct but not a disaster and it is not likely. Mostly what I expect to see is that a number of large land mammals will be restricted to living in large nature parks. Environmentalists should stop tossing around doom mongering about extinctions, none of it is based on fact.

Man, that's the dumbest thing you've ever said. I expect dumb stuff like this from the conservative right wing nut jobs that post comments here, but somehow you saying crap like this surprised me. The rate of extinction is accelerating. This is a fact, not a theory. The theory is that mankind is the cause.